A disk drive assembly is a computer, mass-storage device from which data may be read and/or to which such data may be written. Typically, a disk drive assembly includes one or more randomly-accessible rotatable storage media, or disks, upon which the data is encoded by various means. In a magnetic disk drive, the data is encoded thereon as bits of information comprising magnetic field reversals grouped in tracks on the magnetically-hard surface of the rotating disk or disks. When the disk drive assembly includes a plurality of disks, the disks are typically stacked in a generally parallel and spaced relationship and affixed at their inner-diameters to a common hub.
A spindle motor imparts rotational forces to rotate the rotatable storage media at a rotational speed. A head transducer, such as a magnetoresistive sensor is positionable proximate to the rotating storage media to read the data from the magnetic media forming the storage media. The magnetoresistive sensor detects magnetic field signal changes from the magnetic media. Such detection is made due to changes in the resistance of the magnetoresistive sensor responsive to changes in the direction and amount of magnetic field being sensed by the sensor.
The magnetoresistive sensor is supported by an actuator arm. Movement is imparted to the actuator arm and, hence, to the magnetoresistive sensor by appropriate actuation of a voice coil motor of an actuator assembly. Successive read and write operations can be selectively performed by suitably positioning and repositioning the magnetoresistive sensor, and associated inductive write transducer, proximate to selected locations of the storage media.
Advancements in technology have permitted the development and implementation of successive generations of disk drive assemblies of ever-improving performance characteristics and memory capacities by employing ever-smaller physical sizes for the critical dimensions in the drive components.
Several problems inherent to a disk drive assembly become increasingly problematical, however, when attempts are made to provide a disk drive assembly of improved performance and increased memory capacity, with smaller sizes for critical dimensions in the drive components.
One such problem pertains to asperities. An asperity is formed, e.g., by a particulate positioned, sometimes not fixedly, upon the magnetic storage media. An asperity can also be formed by a surface irregularity of the storage media. Such an asperity can result in a collision with the magnetoresistive sensor as the location at which the asperity is positioned is rotated into proximity with the sensor. When a collision occurs, thermal energy is generated and is imparted to the sensor, thereby causing a temperature increase of the sensor.
A magnetoresistive sensor is susceptible to damage as a result of such temperature increase. As magnetoresistive sensors are constructed to be of increasingly smaller sizes, the thermal energy imparted by a thermal asperity to a smaller-sized, magnetoresistive sensor shall become an increasingly significant problem. Viz., as the same amount of thermal energy is imparted to a sensor of reduced size, the temperature increase of the sensor shall be correspondingly greater.
In at least one construction of a magnetoresistive sensor, the sensor includes an antiferromagnetic (AFM) layer which is used to pin a pinned layer of the sensor by way of an exchange magnetic field. If the thermal energy imparted to the magnetoresistive sensor is great enough such that the AFM layer approaches or exceeds its Neel temperature, irreversible damage to the magnetoresistive sensor might occur. Subsequent to the thermal asperity event, the AFM layer of the magnetoresistive sensor cools. But, such cooling occurs in the presence of a random magnetic field associated with the magnetic field emanating from the magnetic storage media. Such magnetic field emanating from the disk might alter the resultant orientation of the magnetic exchange field of the AFM layer. And, such changed orientation might permanently alter the transfer curve of the magnetoresistive sensor and its resultant output signal. If extensive, such alteration might destroy the operability of the magnetoresistive sensor.
A manner by which to protect the magnetoresistive sensor from damage due to a thermal asperity event advantageously shall increase the reliability of a disk drive assembly, or other computer mass storage device, in which the magnetoresistive sensor is embodied.
It is in light of this background information related to magnetoresistive sensors that the significant improvements of the present invention have evolved.